1. Field of the Invention
The present invention relates to the optical detection of the characteristics or features of a surface, including but not limited to anomalies or contaminants which can be found on such surface. Furthermore, the present invention relates to the method and apparatus which detects light reflected or scattered from the entire surface subject to heterogeneous condensation of a vapor and evaporation in order to reveal the surface characteristics of the surface without destroying the surface itself.
2. Description of the Art
The inspection of the surface features of a wafer is a critical step in the manufacturing process of microelectronic devices because contamination is a source of loss of yield during the manufacturing process. Typically, wafers are inspected repeatedly during the manufacturing process. As the size of the device features shrinks, the detection of such features as well as anomalies on the wafers themselves becomes increasingly difficult using conventional optical methods. In addition, these conventional methods are generally slow since many times only a portion of the wafer is scanned.
Optical instruments have long been used to detect, locate and size particles on semiconductor wafers. Generally, the practical detection limit of particles on bare silicon wafers is about 0.1 to 0.2 micrometers. Since the amount of scattered light from a particle is proportional to d6, where d is the particle diameter, a reduction in particle size by a factor of 2 results in a 64-fold decrease in scattered light. As a detection rate of about one to three wafers per minute is generally desired, and the number of photons scattered from a light source falls into the range of about 0.1 micrometers, detection becomes very difficult with conventional devices. Even at these small sizes, anomalies or contaminants can be detrimental to the surface and even the entire device itself. Once a contaminant, defect, anomaly or uncharacteristic feature is found, the entire batch of wafers may have to be reworked or disposed of.
U.S. Pat. No. 3,580,066 to Pliskin describes a method of determining the completeness of oxide etching of via holes in a silicon member surface, in which the silicon member is cooled while a stream of moist gas is directed onto its surface. The stream of moist gas is produced by bubbling dry nitrogen through de-ionized water. Condensation in the holes is in the form of a thin film over residual oxide but beads into droplets over bare silicon.
U.S. Pat. No. 4,314,474 to Dermarderosian describes a method in which an inert fluorocarbon vapor is condensed on a test surface in order to detect cracks, fissures and other such faults on the surface. A liquid fluorocarbon contained in a flask is heated to a gentle boil while an inert gas, such as air or nitrogen, is bubbled through the liquid. A mild flow of vapor is carried from the flask to the test surface by a vapor tube, the free end of which is held from about xc2xd inch to 1 inch (approx. 2 cm) away from the test surface. The fluorocarbon has a surface tension sufficiently low that as it condenses it wets the surface, forming a layer of uniform thickness. Detection is visual and may be made with the aid of a microscope and relies on the fact that faulted regions absorb comparatively more of the incident light than unfaulted regions. Defects on the order of one micrometer in size are visible.
U.S. Pat. No. 4,967,095 discloses a method and apparatus for detecting and classifying particles on a surface using condensation. The apparatus includes a heatable wick disposed over a test surface and in fluid communication with a source of volatile liquid. A zone of vapor supersaturation is created on the surface in which condensation on the particles of the surface can occur. A light beam is directed onto the surface. The droplets are detected by means of light scattered from the droplets.
U.S. Pat. No. 5,608,155 to Ye et al., discloses a method to enlarge the apparent size of sub-micron contaminant particles on a substrate by selective condensation of a vapor on the substrate. The substrate is apparently located proximate to and spaced apart from a liquid vapor source that is heated. The vaporized liquid apparently adheres to the particles and according to the patentee, after a predetermined period of time, condensation of the vapor on the substrate is stopped. The substrate is scanned for detecting the particles.
A need still exists for a simple apparatus and method to determine the surface characteristics or features of an entire surface which is nondestructive and which can quickly show the surface characteristics.